1. Field of the Invention
The present invention relates to an image forming apparatus.
2. Description of the Related Art
Typically, a direct transfer method or an indirect transfer method is employed in color image forming apparatuses for transferring images to a recording medium. In the direct transfer method, toner images of different colors are formed on a plurality of photosensitive elements, and those toner images are then directly transferred onto a recording medium (hereinafter, “sheet”) in a superimposed manner thereby forming a color image on the recording medium. On the other hand, in the indirect transfer method, a toner image of a specific color is formed on each of a plurality of photosensitive elements, those toner images are first transferred onto an intermediate transfer belt in a superimposed manner thereby forming a color image on the intermediate transfer belt, and then, the color image is transferred from the intermediate transfer belt onto a sheet.
Generally, image forming apparatuses employing the indirect transfer method include, apart from the intermediate transfer belt, a secondary transfer roller, and an opposing roller. The secondary transfer roller and the opposing roller are arranged parallel to each other in an abutting manner with the intermediate transfer belt interposed therebetween. The intermediate transfer belt and the secondary transfer roller are pressed against each other, and a sheet is passed through a nip, i.e., a transfer nip, between the intermediate transfer belt and the secondary transfer roller. Because of this arrangement, toner images on the intermediate transfer belt are transferred onto the sheet as the sheet passes through the transfer nip.
Japanese Patent Application Laid-open No. 2002-296927 discloses a conventional image forming apparatus in which a secondary transfer roller is integrally attached to an openable and closable cover (movable case), and an intermediate transfer belt is arranged in a main body of the image forming apparatus. With this configuration, it is easier to perform maintenance work, or remove jammed sheets. When the cover is opened, the secondary transfer roller separates from the intermediate transfer belt, so that it is possible to quickly and easily remove sheets jammed in the transfer nip. Furthermore, when the cover is opened, the intermediate transfer belt is exposed to the outside, so that repair or replacement of the intermediate transfer belt can be performed quickly and easily. When the cover is in a closed state, the secondary transfer roller is biased toward the intermediate transfer belt by a spring arranged on the cover, so that the secondary transfer roller and the intermediate transfer belt are pressed against each other.
In the conventional image forming apparatus, however, the spring for biasing the secondary transfer roller is attached to the cover. Therefore, a pressure applied from the secondary transfer roller to the intermediate transfer belt changes if the cover is not in a desired closed position. If the pressure applied from the secondary transfer roller to the intermediate transfer belt is nonuniform, sheets may not enter in the transfer nip in a desired manner, or images may not be transferred onto sheets in a desired manner.